for flying with a firearm, handguns must be in carry-on luggage, and be in a locked container separated from any ammunition. firearms must also be declared to the TSA, who can elect at any time to inspect the handgun for compliance. note that there is no regulation that stipulates a "TSA approved" lock. those luggage locks are generally extremely poor security. get a good Abloy lock on a Hardigg/Pelican case and force the TSA to ask you to unlock it. do not use a soft case. if a hard case is too expensive, look for cheap musical instrument cases in your area.